There exists an intimate and mutually-reinforcing relationship between linguistic and biological diversity. In order to safeguard biological diversity, then, it is vital also that we find ways to protect linguistic diversity under international law – as a common heritage – while also seeking national language policies that encourage it. There are approximately 6,800 different languages worldwide, of which the large majority are indigenous. Many of these are endangered and 6,500 of these languages are spoken by only 10% of the world’s population, placing many of them in a situation of extreme endangerment: as many as 90% will become extinct by the next century. Biological diversity faces a similarly dramatic decline and so it is a matter of extreme urgency to respond to various factors – including language loss – that contribute to this. This article aims to present the relationship of linguistic and biological diversity – with an emphasis on local and indigenous languages – in a way that can provide the basis for law- and policy-making. In so doing, it will also provide an analysis of the existing international law national policy frameworks relevant to the effective safeguarding of linguistic diversity and, in particular, with a view to fostering the contribution of the world’s languages to preserving biodiversity.